Thermostat



July 30, 1946. K. L. wooDMAN 2,495,003

THERMOSTAT original Fiied sept. 17, 1941 INVENTOR A/erme L. Nava/mon.

Empemure Patented July 30, 1946 THERMOSTAT Kenneth L. Woodman, Manseld,Ohio, assignor to Westinghouse Electric Corporation, East Pittsburgh,Pa., a corporation of Pennsylvania Original application September 17,1941, Serial No. 411,112. Divided and this application June 14, 1944,Serial No. 540,355

6 Claims.

My invention relates to electric percolators and, more particularly, toan automatic temperature control for electric percolators. Thisapplication is a division of my copending application, Serial No.411,112, iiled September 17, 1941.

Itis an object of my invention to provide a control for an electriccoffee maker or percolator which will automatically cause the heatingelement to provide ahigh or coiee brewing temperature and then toautomatically reduce the heat output of the heating element to suchvalue that it will maintain the brewed coffee at a serving temperaturesubstantially below that of the brewing temperature.

It is a further object of my invention to provide a coffee maker orpercolator heating stand having a thermostatic structure therein, inheat relationship with a heating element, which is adapted toautomatically control the output of such heating element for producing ahigh heat output for a predetermined time and then to produce asubstantially lower heat outputl as long as the heating element isconnected to a suitable power supply.

It is another object of my invention to provide a simple, inexpensivecolee maker or percolator heating stand which embodies an automatictemperature control structure for maintaining a brewing temperaturethroughout a predetermined selective time depending upon the quantity ofcoffee to be brewed and for automatically reducing the temperature ofsuch coffee so as to maintain it at a, desired temperature.

It is still another object of my invention to provide a control for anelectric coffee maker which will cause the heating element to provide ahigh heat output during a predetermined liquid heating period,deenergize the heating element for a predetermined time period to permitproper infusion of the coiee, and intermittently energize the heatingelement to maintain a predetermined low heat output thereafter.

It is still a further object of my invention to provide a percolatorheating stand having a thermostatic control for regulating the heatoutput of a heating element incorporated therewith which has adjustablecontrol means operable by an operator, whereby when the coffee hasbreweda desired length of time, such control means may be operated so asto permit the thermostatic structure to maintain the temperature of suchbrewed coiee at a'predetermined serving temperature.

Other objects of my invention will either be pointed out specifically inthe course of the following description of a device embodyingmyinvention, or will be apparent from the description taken in conjunctionwith the accompanying drawing, in which:

Figure 1 is an elevational View partly in section of a coffee makerincorporated with a, heating stand embodying my invention;

Fig. 2 is a partial sectional view taken along the line II-II of Fig. 4;

Fig. 3 is a partial plane View of the heating stand of Fig. 2;

Fig. 4 is an enlarged sectional View of the heating stand embodying myinvention taken along the line IV-IV of Fig. l;

Fig. 5 is a graph having curves illustrating the operatingcharacteristics of the heating element and thermostatic controlembodying my invention;

Fig. 6 is a view similar to Fig. 2 illustrating a modied form of myinvention; and

Fig. '7 is a. partial side View taken along the line VII-VII of Fig. 6.

Referring to the accompanying drawing, in which like referencecharacters indicate like parts in the several figures, there isillustrated a coffee maker or percolator which may be of any well knowntype I0 having a heating stand I2 which comprises an exterior casing I4,a heating unit I5, and a thermostatic structure I8 responsive to theheat developed by the heating unit I5 for regulating the operation ofsuch element. The thermostatic structure I8 comprises a iirst heatresponsive device 20, a second heat responsive device 22, and a controlmeans 24 therefor.

The coffee maker or percolator I0, which may be of any well known type,has a lower vessel which rests upon the heating stand I2 in directcontact with the heating unit I5 for a purpose hereinafter described andan upper vessel which is adapted, through the agency of a gasketV totightly iit within such lower vessel. The lower vessel normally retainswater to be heated, while the upper vessel is adapted to retain theground coffee in keeping with established practice. The water or liquidin the lower vessel is forced upwardly, due to the increase in pressuretherein as such liquid is heated, say, by means of applicants heatingstand I2', into the upper vessel, in which place infusion with theground coiee or grounds takes place, in a well known manner. Thetemperature of the lower vessel is then lowered to permit the passage ofthe brewed coiee back down into the lower vessel, as hereinafterdescribed. l

The heating stand I2 comprises, in this instance, a substantiallycylindrically shaped Vcasce n.9 ing I4 having a centrally depressed topportion le which receives the heating unit l5 and a bottom plate 2lextending across the bottom portion of and attached to said casing I4.The eX- terior casing Ill is preferably formed of any light weight sheetmaterial. A plurality of apertures 23 and 2'3 are located within the topportion I9 and bottom plate 2l, respectively, to provide a passage forthe flow of air through the heating stand i2 and about the heating unitl5 for cooling said unit, as hereinafter described.

The heating unit I5 comprises, in this instance, a ilat plate ordisc-shaped member I7 formed of an insulating material, such asporcelain, having spiral grooves in its upper surface for receivingmember 22 operates in a normal manner flexing suitable electricalresistance heating elements IS.

The flat insulating brick or plate I7 is retained slightly above the topsurface of the top portion i9 of the casing i4 to permit air passingthrough said casing to come in contact with said plate to cool it ashereinafter described. The resistance element i@ of the heating unit I5is connected to a suitable power supply, not shown, by means of wellknown prong receptacle members 26 and is connected in series with thethermostatic structure I8 which is in thermal communication therewith.

rIhe thermostatic structure IB embodies the rst heat responsive device2@ and the second heat responsive device 22 which are rigidly attachedto a heat conducting Supporting bracket 28 which is attached to thedepressed top portion I9 and to the bottom plate 2l of the casing I4.The bracket 28 is formed of good heat conducting material and is rigidlyattached, say, by spot welding, to the top portion I 9 of the casing I4which, in turn, supports the heating element I6, The bracket 28,therefore, provides a good heat conducting path from the heating unit I5to the thermostatic structure i8. The thermostatic structure I S3 thusreceives its heat from the heating unit and not directly from the'lowerVessel, and through the variations in temperature of such heating unitcontrols the operations thereof.

The rst heat responsive device 2U is, in this instance, a snap actingbimetallic element, preferably of the type disclosed in the ValverdePatent 1,980,167. Said element is rigidly attached at one end thereof tothe heat conducting bracket 2S by means of a suitable supporting member13D (see Fig. 2). It will be noted that the free end of device 2&3 isconnected through plunger member 3Q and the free end of the secondheat-responsive device 22 to jumper member 35 which engages stationarycontacts ('36, in circuit with the heating element I6. For purposes ofclarity and convenience, therefore, thermostatic device 29 will beherein referred to as having an open and a closed position,respectively, corresponding to the open and the closed position ofmovable -jumper or contact member 35. The bimetallic element or rst heatresponsive device 20 has an adjustable opening temperature. I-Iowever,the closing temperature of element 2i) remains substantially below thatof the serving temperature of the brewed coffee and somewhat above theroom temperature. Accordingly, the thermostatic element 2b will alwaysbe in a closed position at room temperature. However, it will remainopen while the brewed coffee is at the serving temperature. Thebimetallic element or first heat responsive device 20 has a centrallylocated stud-like member 32 rigidly attached thereto for receiving theadjustable control.means-24,.as hereinafter described. In addia purposehereinafter described.

open and closed so as to maintain the brewed coiiee at its servingtemperature. However, member 22 opens at a lower temperature anddevelops less flexing power than member 20, for A loosely mounted jumpermember 35 is attached to the movable end of the bimetallic element 22 soas to engage stationary contacts 3S to energize or deenergize theheating unit I5 in a manner hereinafter described.

The first and second bimetallic members 20 and 22, respectively, arepositioned substantially in line with each other so that, when the rstmember 2@ which develops a greater flexing force than the second element22, is in its closed position, the plunger member 35, attached to thefirst member, will engage and retain the second bimetallic member in acontact closed or engaged position, until the first bimetallic membersnaps toits open or high heat position. Accordingly, it follows thatsince the flexing force of the second bimetallic element 22 is somewhatless than that of the first bimetallic element 2S the first bimetallicelement 2t controls or determines the position maintained by the secondbimetallic element.

The manual control or adjusting means -24 comprises, in this instance,an elongated shaft 38 having an inner threaded end portion whichthreadedly engages the member 32 attached to the element 2i). A controlknob ll positioned outside the casing I4 is attached to the outer end ofshaft 38 whereby the operator may selectively determine the rotativeposition of the shaft 38. As the control knob 4i) is rotated by anoperator, the shaft 38 through its threaded engagement with member 32determines the longitudinal position of member 32 and of the mid pointof the bimetallic element 20, This selective positioning of the midpointof element 20 determines or varies the opening temperature of suchelement, in accordance with well known teachings, and, in turn, ashereinafter described, controls the operation of the coffee-makingprocess.

When operating the coffee maker heater stand I2 embodying my invention,the coffee vessels are positioned thereon in a manner similar to thatillustrated in Fig. 1. Water is rst placed within the lower vessel andthe coffee bean or grounds within the upper vessel, with the lowervessel being sealed by the upper vessel and its gasket in a well knownmanner. The heating unit I5 is then connected to a suitable power supply(not shown) by means of any well kno-Wn cord and plug arrangement, alsonot shown. The heating unit I5 thus, upon heating, increases thetemperature of the lower vessel and the fluid therein. Inasmuch as thethermostatic structure is initially at room temperature such structureis in a closed or contact engaged position, due to the firstthermostatic element 2i) being in its closed or low temperatureposition, Vsimilar to' that shown in Fig. 2. The heating unit` uponcontinued operation increases the temperature of the liquid inthe lowervessel until the increasing pressure produced by the heated liquidforces such liquid upwardly into the upper vessel, in a well knownmanner. The heat output of the heating unit at the time the liquid movesinto the upper vessel is of such value as to cause the firstthermostatic element 20 to snap to its open position. The heating unit Iis then deenergized, inasmuch as the second bimetallic element 22 opensat a lower temperature and, accordingly, opens with the rst bimetallicelement 2i). It is to Abe understood that the control knob 40, and,therefore the thermostat 20 are selectively adjustable by an operator tocorrespond to the quantity of water in the lower vessel. Accordingly,the temperature required for causing the first element 20 to operatewill vary with the amount of liquid positioned within the lower vessel.In other words, the operator after having lplaced a predetermined amountof water within the lower vessel, say, for example, six cups, thenrotates the dial 40 to the six-cup position (see Fig. 3) The heat outputof the heating unit I5 is thus of such character as to just raisesubstantially six-cups of liquid to the upper vessel by the time thefirst bimetallic element snaps Open.

If it be desired to have either a weak or strong coffee, the controlknob 4i) may be positioned either below or above the six-cup position,respectively. This, in turn, regulates the temperature of the liquid inthe lower Vessel and, accordingly, the pressure produced thereby.

With the liquid elevated to the upper position, infusion takes placewith the coffee bean or grounds. Then as the temperature of the lowervessel and heating element decrease the brewed coffee descends to thelower vessel. The first bimetallic element 23, being capable ofreturning to its closed position only at a point below the servingtemperature, remains open. However, the second thermostatic element 22oscillates between its open and closed position independent of the firstelement 20 so as to maintain the heat output of the heating unit I5 atsuch value as to maintain the coffee temperature at its servingtemperature of, say, substantially 175 Fahrenheit.

The infusion time is a function of the thermal storage capacity of theheating unit I5 and the rate of cooling thereof. The infusion timeshould be as short as possible for a good coffee brew. To reduce theinfusion time period to a minimum, the lower vessel is left in directcontact with the heater. By leaving the lower Vessel in contact with theplate I1 of the heating unit I5 said structures cool faster than whenthe vessel is raised above the heating unit. This is due to the fastertransmission of heat from the unit I5 to the small amount of liquidremaining in the bottom vessel and the faster dissipation of this heatby the vaporization of the liquid than the mere radiation of heat fromthe unit I5 and coffee vessel when the vessel is removed from the unit.

Accordingly, by leaving the bottom vessel in direct contact with theheating unit plate I'I, by controlling the weight of said plate, andsecuring circulation of air on the bottom and sides of the heater plate(see arrows Fig. 4 which represent the flow of air through the heatingstand I2), the infusion time may be accurately controlled. A shortinfusion period may thus be acquired so as to obtain the optimum incoffee making efficiency.

Referring to Fig. 5, I show a temperature-time curve of the thermostaticstructure I8 and bimetallic elements 20 and 22, illustrated by curve OX,and of the water positioned within the lower vessel, illustrated by thecurves OR. With the six-cup setting of the control knob 4), ashereinabove described, the bimetallic elements increase in temperaturealong the line OX to a temperature as illustrated by the dotted line E,at which point the thermostat 20 will snap open, deenergizing theheating element. At this time the temperature of the water issubstantially above that of the serving temperature, as illustrated bycurve OR and dotted line Z, and will have passed into the upper vessel.Due to the nthermal storage capacity of the heating unit including theporcelain plate I1 as well as that of the lower vessel of the percolatorI0, a predetermined time B' will pass between said deenergization of theheating element, and the reenergization of the heating element due tothe closing of the second bimetallic element 22. During this infusiontime B' the fluid in the upper vessel cools and returns to the lowervessel. Afterv the second bimetallic element 22 has become re-. engaged,such element intermittently energizes the heating element I5 whichmaintains the ternperature of the bimetallic elements 20 and 22 at thatillustrated by Y on Fig. 5. This, in turn, maintains the temperature ofthe brewed coffee at substantially that illustrated by the dotted line Zor the curve OR.

It is, therefore, obvious that the described thermostatic controlmechanism for a coffee maker' stand provides automatic means for heatingthe water within a coffee maker .up to its brewing temperature, and,then, after a predetermined infusion or brewing period, automaticallyregulates the energization of the heating element to maintain the brewedcoffee at a predetermined serving temperature.

Referring to Figs. 6 and '7, a modified form of thermostatic controlstructure Ida embodying my invention is illustrated. As will be noted,,a single thermostatic element, namely, the heretofore so-called secondbimetallic element 22, is employed. However, the control means 24a, hasa cam shaped member 3l attached to the inner end of the control shaft38. The cam 3| is adapted to engage a pin 21 rigidly attached tosubstantially the midpoint of a ,bimetallic element 22. The cam 3lengaging the pin 21 retains the bimetallic element 22 in its contactengagement or closed position during the time the heating element isinitially energized or during the time in which the unbrewed water isinitially within the lower vessel. Then, as the water moves from thelower vessel to the upper vessel so as to permit infusion of the brewtherein, the operator merely rotates the control knob 40 so as to permitthe bimetallic element 22 to operate in its normal manner. Suchbimetallic element thus permits the temperature of the heating elementI6 to return to substantially that illustrated by the dotted line Y inFig. 5, during the infusion period B', whereupon the bimetallic element22 maintains the energization of the heating element so as to insure thetemperature of the brewed coffee being retained at substantially theserving temperature illustrated by dotted line Z, as hereinabovedescribed.

Itis, therefore, obvious that applicant has provided in his modifiedstructure a control means for insuring a coiTee brew to be first broughtup to its brewing temperature, and then, upon the operation of thecontrol means by an operator, for maintaining such brewed coffee at thedesired serving temperature.

It is further obvious that with the structure as set forth herein, it ispossible to ensure a predetermined infusion period during the coieemaking cycle so as to obtain uniform and satisfactory results whenbrewing coiifee.

While this invention is shown in but two forms, it will be obvious tothose skilled in the art that it is not so limited but it is susceptibleto various other changes and modifications without departing from thespirit thereof and it is desired, therefore, that only such limitationsshall be placed thereon as are specifically set forth in the appendedclaims.

I claim as my invention:

1. A thermostat for an appliance comprising a first thermostatic memberand a second thermostatic member, both members being actuated in thesame direction upon an increase in temperature, said first member beinginherently snap-acting and, when in a closed position, engaging thesecond member for retaining it in a closed position until the rst membersnaps to its open position.

2. A thermostat for an appliance comprising a snap-actingthermal-responsive member closing at a temperature below 175 F., asecond thermal-responsive member, both members being actuated in thesame direction upon an increase in temperature, and means moved by therst member engaging said second member for retaining it in a closedposition while the first member remains in a closed position.

3. A thermostat for an appliance comprising a snap-actingthermal-responsive member, a second thermal-responsive member,cooperating contacts operated by said second member, said first memberretaining the second member in a contact closed position when said rstmember' is in its closed position, said second member being free tointermittently operate from one position to another when the firstmember is in an open position.

4. A thermostat comprising a first thermalresponsive member adapted toopen at a given temperature and .remain open until a relatively cooltemperature is reached, a second thermalresponsive member having a loweropening temperature and a higher closing temperature than said firstmember, said first member being disposed to restrain the openingmovement of said second member until said given temperature is reached,and said second member thereupon being adapted to Cycle between itsopening and closing temperature free from restraint by said firstmember.

5. A thermostat comprising a iii-st snap-acting thermal-responsivemember adapted to open at a given temperature and remain open until arelatively cool temperature is reached, a second thermal-responsivemember having a lower opening temperature and a higher closingtemperature than said rst member, said first member being disposed torestrain the opening movement of said second member until said giventemperature is reached, whereupon such restraint is abruptly removed,and said second member thereupon being adapted to cycle between itsopening and closing temperatures free from restraint by said rst member.

6. A thermostat comprising a first snap-acting strip typethermal-responsive member adapted to open at a given temperature andremain open until a relatively cool temperature is reached, a secondslow acting strip type thermal responsive member disposed insubstantially parallel relation to said first member and having a loweropening temperature and a higher closing temperature than said firstmember, said r'st member having one end portion engaging thecorresponding end portion of said second member to restrain the openingmovement of said second member until said given temperature is reached,whereupon such restraint is abruptly removed, and said second memberthereupon being adapted to cycle between its opening andl closingtemperatures free from restraint by said first member,

KENNETH L. WDMAN.

